Safety, tolerability, and pharmacokinetics of a single ascending subcutaneous dose of GSK3772847 in healthy participants

Abstract The aim of this study was to evaluate the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of GSK3772847, compared with placebo administered subcutaneously (SC) in healthy participants, including cohorts of Japanese and Chinese participants. This was a single‐center, randomized, placebo‐controlled, double‐blind, single ascending dose study. Following a screening period of up to 28 days, eligible participants were assigned to one of four cohorts receiving a single dose of GSK3772847 70 mg (cohort 1) or 140 mg (cohorts 2, 3, and 4) or placebo SC. In cohorts 1 and 2, participants were randomly assigned to one of three injection sites (upper arm, abdomen, or thigh), while cohorts 3 and 4 included Japanese and Chinese participants, respectively, assigned to receive GSK3772847 or placebo SC (upper arm). Participants attended follow‐up visits on Days 9, 15, 29, 43, 57, 71, and 85 before final analysis. GSK3772847 was generally well tolerated. Most adverse events (AEs) were mild, resolved without treatment and were considered not related to study treatment by the investigator. There were no serious AEs or deaths during the study. The PK and PD were dose dependent, with negligible differences across injection sites or ethnicities. Target engagement was demonstrated by reduced free soluble interleukin 33 (sIL‐33) concentrations and substantially increased total sIL‐33 concentrations compared with baseline. Subcutaneously administered GSK3772847 was well tolerated in healthy participants, including cohorts of Japanese and Chinese participants, and shows consistent PK and PD across injection sites and ethnicities.

ID 209635/NCT04366349) was to evaluate the safety, tolerability, pharmacokinetics, and pharmacodynamics of single ascending doses of GSK3772847, compared with placebo. GSK3772847 was administered SC in three different injection sites in healthy participants. Cohorts of Japanese and Chinese participants received GSK3772847 SC in the upper arm only.

| Study design and treatments
This Phase 1, single-center, randomized, placebo-controlled, doubleblind, single ascending dose study in healthy participants was conducted in the United States from 21 July 2020 to 21 December 2020. Following a screening period (of up to 28 days), participants who met the eligibility criteria were assigned to one of four cohorts and were randomly allocated within each cohort to receive a single dose of either GSK3772847 or placebo SC ( Figure 1). The site of injection was randomized to the upper arm, abdomen, or thigh for co- On Day 1, participants were assigned a unique randomization number, encoding the participant's assignment to one of the four study arms according to the schedule generated prior to the study. In cohorts 1 and 2, 18 participants were randomly allocated to receive GSK3772847 70 mg (cohort 1) or GSK3772847 140 mg (cohort 2) SC, and six participants to receive placebo SC in each cohort. Participants in cohorts 1 and 2 were also randomized to one of three injection sites (upper arm, abdomen, or thigh). In cohort 3, six Japanese participants were randomly allocated to receive GSK3772847 140 mg SC, and two to receive placebo SC in the upper arm injection site. Finally, in cohort 4, six Chinese participants were randomized to receive GSK3772847 140 mg SC, and two to receive placebo SC in the upper arm injection site. Participants were admitted to the unit the day prior to dosing (Day 0) and were discharged after completion of assessments on Day  The safety population included all randomized participants who received at least one dose of study intervention (analyzed based on treatment received). The PK population included all randomized participants who received at least one dose of study treatment, and for whom at least one post-randomization PK sample was obtained, analyzed, and was measurable. The PD population included all randomized participants who received at least one dose of study treatment, and for whom at least one PD sample was obtained, analyzed, and was measurable.

| Study endpoints and assessments
The primary safety endpoints were the incidence and frequency of adverse events (AEs) and serious adverse events (SAEs), including injection site reactions, and these were summarized descriptively by treatment group and cohort. Further primary endpoints were PK parameters including, but not limited to, area under the plasmaconcentration time curve (AUC), maximum plasma concentration (C max ), time to C max (t max ) and terminal half-life (t1/2) of GSK3772847, summarized by cohort and by injection site.
Secondary endpoints were the maximal decrease from baseline (the last assessment prior to the first study dose) in free soluble IL-33 (sIL-33); a maximal increase from baseline in total sIL-33 levels in serum summarized by cohort (and injection site for cohorts 1 and 2); and the incidence and prevalence of anti-GSK3772847 antibodies and plasma 4β-hydroxycholesterol/cholesterol (4βOHC/C) ratio (pre-treatment and following dosing of GSK3772847), summarized by cohort (and injection site for cohorts 1 and 2) over time.
Other endpoints included 12-lead ECGs, clinical laboratory safety tests, vital signs, blood eosinophil levels, free and total sIL-33 levels in serum, and GSK3772847 levels in the serum, summarized by cohort (and injection site for cohorts 1 and 2) over time. All endpoints were summarized descriptively.

| Sample size and statistical analyses
The sample size was selected to allow estimation of the key PK pa- A total of 64 participants were planned to be randomized to receive GSK3772847 or placebo for a total of 18 evaluable participants on GSK3772847 in cohorts 1 and 2, six Japanese participants in cohort 3, and six Chinese participants in cohort 4. While this study was not designed to determine bioequivalence, the sample size for the critical evaluations of dose and injection site comparisons were in line with appropriate guidance, where the minimum number of participants should not be smaller than 12, (when combined across both doses). 13 All endpoints were summarized descriptively.

| Nomenclature of targets and ligands
Key protein targets and ligands in this article are hyperlinked to corresponding entries in http://www.guide topha rmaco logy.
org, the common portal for data from the IUPHAR/BPS Guide to PHARMACOLOGY, 14 and are permanently archived in the Concise Guide to PHARMACOLOGY 2019/20. [15][16][17] 3 | RE SULTS

| Participant population
Patient disposition is shown in Table S1. Age, years a , mean (SD)  baseline characteristics of study participants are presented in

| Safety results
In total, on-treatment AEs were reported in 13 participants and posttreatment AEs were reported in eight participants during the study (

TA B L E 2 Summary of derived GSK3772847 PK parameters for cohorts 1 and 2 (PK population)
There was a serious quality issue identified during the study, which was reported for investigation to the institutional review board. The investigation showed no impact of any clinical significance for any participants; further details can be found in the Supporting Information.

| Pharmacokinetic results
Visual inspection of the median GSK3772847 serum concentrationtime profiles for both dose levels indicated no appreciable difference across injection sites (Figure 2A,B and Table S3). PK parameters per thigh, abdomen and upper arm injection sites were comparable with overlapping confidence intervals (Figure 2A,B and Table S3).
Therefore, PK parameters were summarized across all injection sites by dose ( Figure 2C and Table 2). Systemic exposure between cohort 1 (70 mg SC) and cohort 2 (140 mg SC), as measured by geometric mean AUC (0-t) increased in a slightly greater than dose-proportional manner, with a 2.5-fold increase in geometric mean for a twofold in-  Table 2 and Table S3). Time of occurrence of C max of GSK3772847 (t max ) between cohorts 1 and 2 were comparable and attained 120 and 130 h post-dose, respectively.
Overall, the geometric mean GSK3772847 serum concentrationtime profiles by cohort for 140 mg SC (upper arm) were comparable, with overlapping confidence intervals ( Figure 3, Table 2, and   Table S3). However, the median GSK3772847 serum concentration exposures were marginally but not significantly higher in cohort 3 (Japanese, upper arm) participants (geometric mean AUC (0-t) 13 400 h*μg/ml vs. 11 100 in cohort 2 and 11 300 in Chinese participants; Figure 3 and Table S3).

| Pharmacodynamic results
A significant decrease in free sIL-33 levels was seen in GSK3772847 cohorts as compared with placebo cohorts; this decrease was similar across ethnicities in cohorts 2, 3, and 4 over the study duration. The maximum decrease from baseline in free sIL-33 levels (geometric mean) was >93% with GSK3772847 70 mg SC and >95% with GSK3772847 140 mg SC across all injection sites ( Figure 4 and Table S4). The maximum increase from baseline in total sIL-33 levels (geometric mean) was >2100% with GSK3772847 70 mg SC and >3200% with GSK3772847 140 mg SC across all injection sites (Table S5). A significant increase in total sIL-33 levels was seen in GSK3772847 cohorts compared with placebo cohorts. The median total sIL-33 level increased from baseline by the first post-dose assessment (2 h post dose on Day 1) and appeared to pleateau from approximately Day 10 in all cohorts (Figures 4 and 5). The duration of this plateau was dose dependent (Figure 4) with time of maximal increase from Days 15 to 43 across cohorts/inhection sites. The increase in total sIL-33 levels was similar across ethnicities in cohorts 2, 3, and 4 over the study duration ( Figure 5).

| Immunogenicity
No participant receiving GSK3772847 in cohort 1, 2, or 3 tested positive for anti-GSK3772847 binding antibodies in the confirmatory assay. One participant from cohort 4 (Chinese) confirmed positive results for anti-GSK3772847 binding antibodies (titer 80) on Day 57 and Day 85.

| Plasma 4β-hydroxycholesterol/ cholesterol ratio
Plasma 4βOHC/C ratio to baseline was essentially unchanged (~1) over the study duration in all cohorts (Table S6). In previous studies, PK and PD modeling suggested an IV administration of GSK3772847 1 mg/kg every 2 weeks would provide adequate systemic drug exposure for effective inhibition of the IL-33R signaling pathway in 90% of participants. 11 Assessments of serum concentrations over time suggests that the 70 mg SC dose may deliver a similar effect. Furthermore, the safety and tolerability profiles of GSK3772847 were similar in IV and SC administration routes.

F I G U R E 3
As an endogenous marker for CYP3A4 activity, this study assessed changes in the plasma 4βOHC/C ratio. CYP3A4 is a member of the Cytochrome P450 family of enzymes, which catalyze reactions in the metabolism of a large proportion of drugs and contribute to variation in drug pharmacokinetics. [18][19][20] 4βOHC is formed from CYP3A4 and plasma concentrations rise with increased CYP3A4 activity, making it an appropriate marker for CYP3A4 activity that can be assessed non-invasively. 18,19 No changes were observed compared with baseline over the study duration.
Treatment with mAbs, including GSK3772847, may be associ- This was the first study to evaluate the SC dosing of GSK3772847 in healthy volunteers, including cohorts of Japanese and Chinese participants, which assessed the injection site, dose level, and ethnic group impact on PK and PD. Although the number of participants in this study was small, it was sufficiently powered to ensure an adequate understanding of the tolerability of GSK3772847 when dosed subcutaneously and would enable the estimation of the key PK parameters. In summary, GSK3772847 was well tolerated via the SC route, delivered an exposure and target engagement profile consistent with expectations based on data from the IV route 11 and had consistent properties across injection sites and ethnicities.

AUTH O R CO NTR I B UTI O N S
DF, SS, and CN were involved in the conception of the work, and EP, DF, SS, CQZ, and CN contributed to the analysis or interpretation of data. All authors drafted the work or revised it critically for important intellectual content, gave final approval of the version to be published, and agreed to be accountable for all aspects of the work.

ACK N OWLED G M ENTS
This study was funded by GSK (GSK ID: 209635/NCT04366349).
Editorial support (in the form of writing assistance, including preparation of the draft manuscript under the direction and guidance of the authors, collating, and incorporating authors' comments for each draft, assembling tables and figures, grammatical editing and referencing) was provided by Louise Bullen, PhD, and Laura Murch, PhD, of Fishawack Indicia Ltd, part of Fishawack Health, and was funded by GSK.

CO N FLI C T O F I NTE R E S T
EP, SS, DF, CQZ, and CN are employees of GSK and hold stocks/ shares.

DATA AVA I L A B I L I T Y S TAT E M E N T
Information on GSK's data sharing commitments and requesting access to anonymized individual participant data and associated documents can be found at https://prote ct-eu.mimec ast.com/s/ y tNzC vo7y S y4kP w t Q Tep c?domai n =clini calst udyda tareq uest.

PATI ENT CO N S ENT
All patients provided written informed consent prior to study participation.